sunil somalwar university - lawrence berkeley national ... · – susy models only as vague guides...

Search for Anomalous Production of

Multileptons at CMS with 5.0 fb‐1 of 7 TeV Data

Sunil Somalwar

Rutgers University

June 19, 2012 Sunil Somalwar, Rutgers 1

Outline• SUSY by analogy

• SUSY status & search strategies: an eclectic viewpoint

• Multileptons– Multi‐binned search for anomalous production

of three or more leptons (including hadronic tau’s)

– “Backgrounds ‘R’ Us”

– Unified “Signal” and “Control” regions

– Many funny things happened on the way to the forum

– Results

• SUSY search strategy reprise / Interpretations


Supersymmetry Motivation by Analogy

Doubling the spectrum (particle sparticle) is a big price. Occam’s razor? Worked once before: Assembling the electron (Murayama, TASI Lectures)

Electron q=1.6x10-19 Coul , radius < 10-19m[ 200GeV ~ 10-18m re < 10-18m (from ge), LEP 2006: 10 TeV contact interaction re < 10-20m]

Eassembly ~ +q2/re ~ 10,000 MeV but me~ 0.5 MeV

Large negative “bare mass” me = 0.5 MeV = -9999.5 MeV + 10,000 MeV

FIX: Double the particle spectrum! positron i.e., new physics at ~100fm ~1MeVWeisskopf (1939): Eassembly ~ +q2/re cancelled by E vacuum pair ~ -q2/r (e+ from vacuum)

Sunil Somalwar, Rutgers 3June 19, 2012

SUSY: Why?Today: Higgs has the same hierarchy problem.

Radiative loops: MH ~1015 GeV, but Higgs at 100 GeV (EW scale)

Delicate cancellations at 1015 GeV

OR

SUSY at TeV scale

• top loops cancelled by stop loops “hierarchy problem” solution

But SUSY is badly broken. m(selectron) >> 0.5MeV

Sunil Somalwar, Rutgers 4

H H Hf f

June 19, 2012

Occam’s Razor: Particle Physics VersionWe like doubling the particle spectrum.


Twin Blade(electron & positron)

Single Blade (electron)

Multiple Blades(electron, positron, selectron?...)

June 19, 2012

SUSY Search StatusSimple‐minded squarks & gluinos are getting heavy

• Strong production

• Inclusive JET‐MET, no leptons

• Several sub‐searches with MET, Njet, meff (=ST=HT+MET)

• Backgrounds: W+jets, Z+ jets, ttbar, dibosons, QCD, tau decays

Model: Simplified production of gluinos and Gen1,2 squarks decaying to jets +LSP


ATLAS (4.7/fb)

June 19, 2012

LHC vs SUSY Models

Slide Credit: Stephen Martin


e.g. ATLAS SUSY Results

This is a sugra free talk

LHC

June 19, 2012

OK, the LHC beampipe didn’t melt due to strongly produced SUSY.

It is not the end of the world.

Plenty other possibilities and ongoing searches.


Great Expectations

Search for Strong Production of Supersymmetry Using Precision Thermometry of the LHC Beam Pipe Journal of Irreproducible Results.

June 19, 2012


New Physics Search Axes

MET or jets/HT not guaranteed

Jets + MET≥3 Leptons(jets + MET )

Lepton+photon( jets + MET )

≥2 Leptons with SS(jets + MET )

≥2 photon( jets + MET )MET

MET MET

MET MET

Jet Jet

Jet

Jet

Jet JetJet

e/μ/τ

e/μ/τ e/μ/τe/μ/τ

e/μ/τ

e/μ/τ

• GMSB – Best SUSY‐breaking theory we have, gives photons and leptons (*)

• R‐Parity Violation (*)• Electroweak production (*)• Accidents of SUSY mass spectrum (say squeezed)(strong production hijacked by the leptonic sector) (*)

• Tau enrichment (high tan(β)), tau’s are difficult (*)• top quark as a massive blanket hiding new physics• 3rd Generation • Long‐lived sparticles ….

(*) – In this talk


Many Other Search Avenues

June 19, 2012

MultiLepton Production at LHC

• Leptons produced directly from heavy parents or in a long chain of decays


Leptons Directly from Parent Particles

Leptons from Complicated Chain


Multileptons vs Jet‐MET

• Branching fraction to different final states dependant on mass spectra in model. – Below are branching fractions for different SUSY scenarios.

Jets + MET≥3 Leptons(jets + MET )

MET MET

Jet Jet JetJet

e/μ/τ

e/μ/τ e/μ/τ

SUSY Scenario Examples ≥3L ≥2 Jets, 0 L,MET>200

Slepton co‐NLSP (GMSB) ~100% 0%

Leptonic R‐parity violating ~100% 0%

mSUGRA (Mo=60, M1/2=190) ~23% 11.4%

mSUGRA (Mo=200, M1/2=250) ~1.8% 35%


Search Strategy: Multileptons + MET or HT?(Example: Accident of Mass Spectrum)

HT is the scalar sum of jet ET

m(q)‐m(χ1)∼ ∼

Example:slepton co‐NLSP GMSB scenario m(q)=500. Small mass difference can cut off jet production. Leptonic sector captures strong production.

MET is Missing Transverse Energy

Some models have both HT and MET, but some only have HT or MET. Cannot rely on just one of these variables.Lesson: MET/HT binning

THIS IS *NOT* WEAKPRODUCTION although“Weakinos” come with small HT!

ST versus MET/HT BinningST=MET+HT+ΣpT(iso‐leptons) (ATLAS: “Effective Mass”.)

• ST ~insensitive to how parent decays.– Consider two types of RPV SUSY: Leptonic and Hadronic

• MET distributions are very different, but ST is almost the same. – ST Analysis can be sensitive to a wider range of models

• ST gives information about mass scale of the new physics.• Peak is ~ M(parents) ‐ < M(invisible daughters) >


MET misses Hadronic RPV ST Distributions same

MET ST

CMS 2011 5.0 fb‐1 Multileptons(To appear in JHEP any day)

• Two sub‐analyses to cover wide range of scenarios.– Same lepton selection, backgrounds, triggers, code

– ~50 bins in each analysis

– 3 or ≥4 leptons (e, μ, and τ), bin in M(l+l‐) and number OSSF pairs– Different strategies for isolating new physics from SM.

• MET=Missing Transverse Momentum

• HT= ΣpT(jets) , |η|< 2.5 and pT > 40 GeV

• ST=MET+HT+ΣpT(iso‐leptons) (ATLAS: “Effective Mass”.)


HT [GeV]

MET

(GeV

)

200

50

×[Z, no Z]

×[Z, no Z]

“SUSY” Multilepton 2011based on CMS 2010 Analysis:

Phys. Let. B 704 (2011) 411‐433

×[Z, no Z]

×[Z, no Z]

“RPV/Exotic” Multilepton 2011

ST [GeV]0 300 600

×[Z, no Z] ×[Z, no Z] ×[Z, no Z]

PAS:SUS‐11‐013 PAS:EXO‐11‐045

Ambiguous Search/Control Regions

• We know that we don’t know cast a wide net• Cover a wide range of scenarios

– SUSY models only as vague guides • (CMSSM, GMSB, R‐parity violating)

– Selections based on SM background considerations.– Anomalous (nonSM) production in numerous channels.

• Highlights observed on the way:– First ZZ 4μ event

• (animation available on youtube), Oct 10, 2010 (10/10/2010).– And some unusual (unlikely) 4‐lepton event(s). – Hit a forgotten Standard Model background in the Higgs WW searches.

• Wγ* was left out of searches in both ATLAS and CMS• Prompted changes to CMS/ATLAS H WW searches.• Interesting story, more later.


Event Selection• 3 and ≥4 lepton combinations with e, μ, and ≤2 τ’s

– Select on single and dilepton triggers.

– Cut events if M(l+l‐) < 12 GeV ( J/ψ, Upsilon, γ*)– Cut events where M(ll) off Z and M(lll) on Z (only for signal bins with low

ST and MET/HT)

• Bin instead of cut! Poor S/B bins act as control channels. – # Drell Yan candidates (e+e−, μ+μ‐): 4 leptons can be DY=0,1,2

– Is there a Z candidate? M(l+l‐) 75‐105 GeV


nDY = number of Drell‐Yan (OSSF) pairs

Lepton Selection: (e, μ, τ)• Electrons and Muons:

– pT > 8 GeV, |η| < 2.1– Require Relative isolation < 15% and total isolation < 10 GeV

• Isolation for μ(e) is sum of tracker, calo transverse energy in ΔR < 0.3(0.4) • Relative isolation is total isolation divided by lepton pT

• Tau Leptons:– Leptonic decays fall under e/μ– Accept “single prong” hadronic

• Isolated track (no π0 )• HPS Algorithm (with π0)

– Visible pT > 8/15 GeV, |η| < 2.1


35%

11.61%36.54%

15.19%

Lepton\Trigger Type μ e μμ ee e μ

Leading e/μ > 35 > 85 >20 >20 >20

Next‐to‐leading e/μ NA NA >10 >10 >10

Primary Triggers

Background Predictions

• Uniform background treatment of all channels.

• Monte Carlo Predictions (MC)– TTbar and Irreducible backgrounds: WZ+Jets, ZZ+Jets

• Corrected to match efficiency measurements.

• Systematic for kinematics as well as “fake rates” for ttbar.

• Other backgrounds are “Data Driven”– Z+Jets, WW+Jets, W+Jets, QCD

• No MC. Use dilepton data, estimate number of 3rd and 4th

lepton candidates from jets.

– Z+γ Asymmetric Conversion γ e+e‐ or γ μ+μ‐• Estimate number dileptons+photon conversion from data.


Data vs Monte Carlo


t‐tbar Control Regions (not 3‐leptons)

• Example: TTbar in following control data sets– One lepton (pT > 30) + ≥3 jets (≥1 b‐jet), or dilepton 1 e + 1 μ

– ST > 400 GeV

– Test the overall number of TTbar as well as ST tails.

June 19, 2012 Sunil Somalwar, Rutgers 21ST for single‐lepton sample. ST for dilepton e+μ‐ sample.

t‐tbar MC Validation with Data (cont..)

• TTbar has known jet composition (mostly b‐jets)– MC ok for this purpose.

– Semileptonic decays of heavy flavor measured at B‐factories.

• Isolation of leptons from jets in TTbar– 1 lepton + ≥3 jets (≥1 b‐jet), test μ with large impact parameter.

• Require test μ far from leading tagged b‐jet. (ΔR > 0.6)

June 19, 2012 Sunil Somalwar, Rutgers22

Isolation Range

Data MC

0.0‐0.15 10 13

0.0‐inf 733 745

Integrals from Isolation plot:

Isolated Bin(Most important!)

Cross check heavy flavor semileptonic branching fractions

W±Z MC versus Data3 e/μ, Z candidate, and MET > 50 GeV


HT distribution of WZ Number of jets in WZ

Blue hash bands are uncertainties (syst+stat) on background.

Fully Data Driven Backgrounds



• Pick a proxy object to treat like a lepton– Example: track, non‐isolated lepton, loosened ID, etc.

• In control data measure Proxy Fake factor– Proxy Fake factor has many aliases “fake rate”, “Tight Loose

Ratio”, “conversion factor”….• Depends on spectra, flavor, resolution, branching fraction….

– Test in 2nd control set for “closure test”– Apply to a “seed” data set to get prediction in signal region.

• Systematics: Do key features in control data match seed?– Primary source of systematic uncertainty.– Especially important for this analysis!

Basics of (Legitimate) “Data‐Driven” Predictions


• Use 2L data as a seed to predict ≥3L background– Example: 2e to predict 2e1μ background– Effects like pileup are automatically included.

• Apply background estimation procedures to seeds. – Predict fake Tau using isolation side band. (~25% systematic)

• Systematic from how well we understand isolation distribution.

– Predict e or μ from jet using isolated tracks (~15% systematic)• Systematic from how well you understand types of jets in data set.

– Predict asymmetric conversions using photons. (~100% systematic)• Large systematic due to difficulty in testing method beyond control.

Data Driven Predictions

2μIso 2eIsoμIsoeIso

3μ 2μ1e 2e1μ 3e1e1μ1T2μ1T 2e1T

T Tau

Isolated Track e/μ Scale Factor

• Isolated tracks (π±) as proxy for e/μ from jets– Isolation related systematics are ~same as e/μ

– However! Track e/μ sensitive to average jet flavor


Ratio of lepton to track isolation efficiencies. Parameterize in di‐jet

data as a function of Rdxy

Heavy Flavor produces displaced vertices and non‐isolated tracks with large dxy

Rdxy=N(|dxy|>0.02cm)/N(|dxy|<0.02cm)

A sample of pure b‐jets has Rdxy~30%A sample of pure uds jets has Rdxy~3%

Non isolated leptons and tracks measured in seed to reduce dependence on control data.


• Use isolation side band to predict Fakes– Define fT to convert sideband to isolated

Tau Background

Cartoon Isolation Distribution

#ISO #SB= fT x

We measure fT in dijetdata and apply it to nonisolated τ candidates in l+l‐ data.

Isolation Distribution Shape Not Universal!


• Isolation shape can change drastically.– fT changes between dijet and dilepton data!!

Tau Background Problem

Cartoon Isolation Distributions

#ISO #SB= fT x

We need a way to parameterize changes in fT between different data sets.

Need to match dijetdata to conditions in dilepton data.

Hard Jet Spectra

Soft Jet Spectra

fT=25%

fT=9%


• fSB ‐ Control parameter for isolation shape – fSB approaches zero as jets become harder

Tau Background by Parametrization

#SB/(#SB+#OTHER)fSB =

Use fSB to check for changes in the shape of the fake τ isolation distribution.

Hard Jet Spectra

Soft Jet Spectra

fT=25%fSB=48%

fT=9%fSB=5%


• Bin dijet data and plot fT vs fSB• In dilepton use fSB to predict fT

Tau: fT vs fSB(Data)

Hard Jet Spectra Soft Jet Spectra

(Closure)

Photon Conversions


External conversions (in material) removed with the usual tools. But then something happened on the way to the forum….

Note: Muons!

Note Again: 3 muons!!

Asymmetric Photon Conversions to μ+μ‐

• Two types of asymmetric photon conversions:– External: Due to interactions in material, gives only e+e‐

– Internal (Dalitz): Feynman level (γ*) gives e+e‐ and μ+μ‐


• 2011 Observation of Z (3)4μ• Analogous to π0 e+e‐γ• Observe 3μ Z peak (4th μ failed cuts)

• Also W 2μ (+neutrino) (Higgs!)• Wg* ignored in Higgs WW search before this.

arXiv:1110.1368 R. C. Gray et. al.

• Important background for Higgs ~125 GeV

• Searches modified accordingly.

Z μ+

μ+μ‐

μ‐

Internal Conversion shape obtained from μ+μ‐γ

In asymmetric conversion only 3 of 4μ arereconstructed

A textbook plot of tomorrow?


Z 4‐lepton peak(CMS result)

KL e+e‐ e+e‐ Double‐Dalitz peak(1990’s(Halkiadakis/KTeV) Kaon CP)

H ZZ 4‐lepton peak here?

4‐lepton mass

π0 e+e‐ e+e‐ Double‐Dalitz peak(~1960(Plano et al) Parity)

June 19, 2012

5 fb‐1 7 TeV CMS Multilepton Results



Three Lepton ST Distributions with l+l‐

on Z (Sort of “Control”)

ST distribution of three lepton events that have a Z candidate.

If we assume new physics does not come with Z’s, this is a good test of SM predictions.

Yellow: data‐driven

Blue bands: Background uncertainties (syst+stat).


Three Lepton ST Distributions with l+l‐

off Z (Signal Channel)

ST distribution of three lepton events that have a an l+l‐ pair, but does not make a Z.

One of our signal channels. New physics would be seen as an excess of events at large ST

The yellow histograms are data driven predictions.

Blue bands are background uncertainties.


Three Lepton MET Dist with l+l‐ on Z(HT<200 Control Channel)

MET distribution of three lepton events that have a l+l‐ pair that makes a Z.

The yellow and light blue histograms are data driven predictions.

Blue bands are background uncertainties (syst+stat)


Three Lepton MET Dist with l+l‐ off Z(HT<200 Signal Channel)

Sensitive to EWK SUSY (ElectroWeakino)

MET for 3‐lepton events that have a l+l‐ pair that does not make a Z.

The yellow and light blue histograms are data driven predictions.

Blue bands are background uncertainties (syst+stat)


ST‐binned Results (54 channels)(NDY)x(ST)x(llll, lllτ, llττ, lll, llτ, lττ)

Number of Tau candidates (0,1,2)

≥4 Lep

tons

3 Lepton

s

Exclusion contours from a multichannel likelihood from the 54 channels shown here.

The signal model defines which bins are signal bins and which are control bins.

The same background estimation techniques are applied to all bins.

MET vs HT tables later in talk.

4 Lepton (e/μ/τ) ST


Food for thought…

3 Lepton (e/μ/τ) ST


4(e/μ) ST Channels: Backgrounds


3(e/μ) ST Channels: Backgrounds


2(e/μ)+ OneTau ST Analysis



MET/HT “SUSY” Results: 52 Channels(MET)x(HT)x(llll, lllτ, llττ, lll, llτ, lττ)

Number of Tau candidates (0,1,2)

≥4 Lep

tons

3 Lepton

s

Exclusion contours from a multichannel likelihood from the 52 channels shown here.

The signal model defines which bins are signal bins and which are control bins.

The same background estimation techniques are applied to all bins.

Produced from same package as the ST binning.

4 Lepton (e/μ/τ) MET vs HT


Higgsino Z + Goldstino (diZ + MET signature) (Ruderman and Shih)

3 Lepton (e/μ/τ) MET vs HT


EWKino

Higgs background: Spread around.

Increasing tan(β)

Interpretations



Multilepton MET/HT SUSY Signals

GMSB co‐NLSP


GMSB Slepton CO‐NLSP Exclusion


Sleptons share the role of Next to lightest super partner (NLSP) above the gravitino. This results in a multilepton signal.

Strong production dominates

See model description http://lhcnewphysics.org/web/Topology_Sets.html under GMSB slepton co‐NLSP

Contours made using MET vs HT table

GMSB Slepton CO‐NLSP Exclusion


Heavy squarks and gluinos: R‐Parity Violation as an escape valve

• Squarks and gluinos getting heavier in simple scenariosBUT

• R‐Parity Violation can pull the rug from under searches requiring MET because the Lightest Supersymmetric Particle (LSP) decays.

Also, possibly finite lifetimes depending on RPV couplings.


Leptonic and Hadronic RPV


Exclusion using ST ‐ binned Results (MET can be small)

Leptonic RPV Hadronic RPV

λeμτ L‐RPV λuds H‐RPVGluino vs Squark masses in GMSB RPV

Note tau’s (best sensitivity for e/mu)

Electroweak Production

• Squarks and gluinos getting heavier in simple scenarios

• What if weak production beats strong production?

Electroweak production to the rescue?Less copious, so lesser reach in smass.

(cf: classic trilepton SUSY signature from Tevatron Run II).


Electroweak Production


LSP: Lightest Supersymmetric Particle (Stable due to R‐parity)

EW: ElectroweakC: Color(=strong)

June 19, 2012

Electroweakino Simple topology


Search: Require less hadronic activity(CDF trileptons, ~2008) (Dube thesis)

June 19, 2012

EWK production: CMS Multileptons


Contours made using met/ht search channel countsNO MET SHAPE INFO YET (Only bin‐and‐count)

Arrow: with MET shape infolifts up the curve.

Three or more electrons, muons or taus. Up to two tau’s reconstructed.

54‐channel ST table and 52 channel MET/HT results on and off Z

Signal (low‐bkgnd) and control (high bkgnd) channels treated uniformly.

CMS multileptons in this talk:

a) Strong production GMSB slepton co‐NLSP

b) R‐parity Violation (Leptonic)

c) Sensitive to accidents of spectrum (strong production captured by lepton sector)

d) Missing MET: e.g. RPV (Hadronic): ST comes handy

e) Electroweak Production: cut‐and‐count (shown), [fitting MET/MT in progress]

SURPRISES (detailed background studies)

• CMS pristine di‐Z event ~5/pb (2010)

• Very rare four‐lepton event(s) in 2011, still outstanding.

• Trimuon Z and impact on Higgs


Conclusion Part I: CMS Multileptons: A Broad Inclusive Search

June 19, 2012

Reprise: LHC vs SUSY Models

Slide Credit: Stephen Martin


CMS SUSY Results

BUT….

June 19, 2012

New Physics Possibilities: Ways to go


Nascent SUSY

June 19, 2012

SUSY Search Conclusions

– Masses are getting heavy in simple schemes

– All fox holes hardly explored. The hunt continues.

• More off‐the‐beaten‐path ideas coming into focus.

(The particle knight has to step out of the clunky armor)

• Back to the fox chase (rat race?) with 8TeV

• 2013‐14 should bring plenty of fresh insights as well.

• To be followed by a new energy regime in 2015.

• If a search team discovers something, small chance

that it will be the physics model they were looking for.


Rutgers Particle Knight © Scott Thomas

Rumors of SUSY’s demise are greatly exaggerated. Come, Watson, come! The game is afoot.

June 19, 2012

Credits

• Richard Gray, Scott Thomas, Hitoshi Murayama, Stephen Martin, Konstantin Matchev.

• LHC staff.

• CMS collaborators, conveners and leaders.

• Unknown photographers of penguins and painters of foxes.


Extra Slides



Multilepton MET/HT SUSY Signals

DPS issues in SUSY searches?

A quick digression due to the Double parton scattering (DPS) discussion yesterday:

σ(AB)DPS ~ 100(σA)(σB/barn) @7TeV

σ(ttbar) ~160pb, σ(W) ~30nb

σ(ttW)DPS ~ 0.5fb vs σ(ttW) ~ 150fb

(kinematic dependence caveats?)


1(e/μ)+2Tau ST Analysis


sunil somalwar university - lawrence berkeley national ... · – susy models only as vague guides...

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